Capacitive sensors or capacitance sensors, respectively, for example, serve for detecting the presence of persons or objects in a room or spatial area to be monitored. Capacitance sensors generate electric fields between two or more electrodes. What is measured is a change of an electric field by the change of a capacitive coupling between the electrodes when introducing an object, when changing a composition of a body in the field or when changing an electric coupling to a surrounding mass potential.
Further examples of the application of capacitance sensors are, for example, tank level meters, quality surveillance sensors, inclination angle sensors, flow rate sensors based on tomography principles, sensors for clamping protection, interior and exterior surveillance or touchpads for actuators.
The measurement accuracies that may be achieved by capacitive sensors or the possible detection ranges substantially depend on a signal-to-noise ratio of the electric field measurement. On the one hand, a noise of a transmitter and a noise of a receiver contribute to the noise component of detected signals. This noise may be well controlled by measures in circuit design. On the other hand, however, environmental noise also occurs, which originates from other electric or electromagnetic field sources, respectively, in the surroundings. In order to be able to guarantee high signal-to-noise ratios especially in high interference environments, like, e.g., cars, there is thus a need to increase the electric or electromagnetic field strength, respectively, of a capacitive sensor system as far as possible without exceeding certain limits for electromagnetic radiation. Further, interferences from strong couplings or launchings of external signal sources are to be avoided as best as possible.